Electrical components, especially those used as part of power devices, can often generate significant heat during operation. Because high temperatures can degrade the performance of (or even cause the failure of) many electrical components, assemblies that use such heat-generating components must be able to dissipate heat well enough to maintain acceptable performance of the electrical component.
Many different techniques can be used to provide cooling of electrical components. For example, circulation of air within a housing can be sufficient to cool some types of electrical components contained within the housing. Some electrical assemblies further include physical features (e.g., cooling fins) that increase the surface area exposed to convective air currents, or provide fans to circulate the air further, providing further cooling. This air cooling can be insufficient, however, for high power circuits and/or densely packed circuits.
High power and/or densely packed circuits can need additional heat dissipation, such as by mounting some or all of the electrical components to a thermal dissipation member such as a “cold plate,” thermal pad, heat spreader, dissipater, evaporator, or other type of heat sink. The thermal dissipation member can, for example, be made using one or more materials having high thermal conductivity (e.g., metals such as copper and aluminum). The thermal dissipation member is able to conduct heat away from the electrical device and into the environment via contact between the thermal dissipation member and a structure designed to transfer the heat to the surrounding air or a liquid via conduction and convection. In some instances, a series of thermal dissipation members work together to provide cooling.
DC/DC converter power supplies are an example of an electrical assembly capable of generating significant heat. In one example, DC/DC converter power supplies used with a phased-array radar system currently are made using an assembly in which dielectric material is attached to a metal baseplate. The power components (e.g., power amplifiers, power transistors, rectifiers, transformers, etc.) also are coupled to the baseplate. The metal base of the baseplate efficiently transfers the heat from the high dissipating components to the edges of the baseplate, where the edges of the baseplate are coupled to a heat sink in a higher level assembly that help to provide further cooling. These illustrative DC/DC converter power supplies use aluminum as the baseplate material. An aluminum baseplate is considerably better at transferring heat to the edges of a baseplate than dielectric material alone, but aluminum still has some thermal limitations. Because of aluminum's thermal limitations, in some instances it is necessary to break up a single higher power DC/DC converter into multiple lower power designs, resulting in higher cost and weight.
One known technique for reducing the temperature of the electric devices is by coupling the electric devices to heat sinks with graphite and/or aluminum added to the heat sink which increases the thermal conductivity of the entire beat sink, such as described in U.S. Pat. No. 6,075,701, which is incorporated herein in its entirety. The '701 patent describes embedding a layer of pyrolytic graphite within an aluminum casing having top and bottom sides such that the pyrolytic graphite intimately contacts an interior wall of the aluminum casing. Electrical components can be affixed directly to a top side of the casing, and a heat sink is affixed to the bottom side of the casing, such that heat generated by the electrical component can flow vertically downward from the electrical component, through the casing and embedded pyrolytic graphite, and into the heat sink. However, heat sinks or cold plates with added graphite and/or aluminum to increase the thermal conductivity of the heat sink or cold plate increase the size, weight, and cost of the device.
In some types of electronic devices, such as DC-DC converters, certain components are known to contribute significantly more heat than other components. For example, in some DC/DC converters, the design is driven by two high heat-dissipating components: the main transformer and the output rectifier. Using a standard aluminum baseplate, the temperature rise from the cooled edge to the component's mounting location is a significant portion of the total allowable temperature rise. In one illustrative device, the temperature rise in the aluminum baseplate alone uses almost 50% of the total allowable temperature rise for the device. In higher power DC/DC converters, that temperature rise alone can exceed the total allowable temperature rise, and a more expensive alternate design must be implemented, a significant portion of the allowable temperature rise from the component locations to the cooled edges comes transformer and output rectifier.